The present invention generally relates to removal of contaminants from a solution. More specifically, the invention relates to removal of chlorinated compounds from aqueous streams, such as groundwater, as well as non-aqueous streams.
Groundwater may typically be significantly contaminated by a wide range of problem pollutants, such as radioisotopes, complex organic molecules and the like. Perhaps the most important class of groundwater pollutants, however, is chlorinated hydrocarbons. Chlorinated hydrocarbons are generally toxic. In addition, chlorinated hydrocarbons may be present in significant levels in groundwater, especially at locations such as military sites and civilian priority sites.
A typical dechlorination reaction in the presence of a noble metal catalyst may be expressed as follows: ##STR1## where R identifies an aliphatic or aromatic hydrocarbon radical. Each chlorine atom of the chlorinated compound is replaced by a hydrogen atom which results in a fully hydrogenated aliphatic or aromatic hydrocarbon and hydrogen chloride. Typically, an organic solvent is not affected by the catalytic dechlorination process. However, unsaturated and/or oxygen-containing organic compounds may react with hydrogen to achieve full saturation or removal of oxygen. Therefore, the final product of catalytic dechlorination consists of the original solvent and dechlorinated, now hydrogenated organic compound.
In aqueous systems, due to the volatility of the chlorinated compounds and a low solubility of hydrogen in water, competition between hydrodechlorination and stripping may take place. The reaction may, therefore, be verified by (1) a decrease of the concentration of chlorinated compound in water; (2) a decrease of pH due to HCl formation; and (3) a formation of saturated hydrocarbon gas.
The widespread use of chlorinated hydrocarbons in the past has resulted in a group of contaminants that tend to persist in the environment and that further tend to resist degradation. Halogenated hydrocarbons, such as, for example, TCE, PCE and the like, are the most important of such groundwater pollutants because of their significant presence in particular areas.
A need, therefore, exists for a system for permanently detoxifying aqueous and/or non-aqueous streams contaminated with chlorinated hydrocarbons and the like as well as for simultaneous recovery/treatment of contaminated solvents.